Proper induction of multiple follicles or oocytes is considered to be very benificial in current in vitro fertilization. In this study the stimulation dosage in relation to the number of follicles, correlation of follicular development including the number or diameter and serum estradiol(E2)levels or response, and fertilizability of the oocytes retrieved according to the serum E2 responses and the terminal E2 patterns will be analysed. The data to be presented are based on 92 cycles in 88 ovulatory infertile patients with average age of 33 years(ranging 24~41) including 76 having tubal factors(salpingectomized, reversal failed or nonfunctioning hydrosalpinx), 5 having endometriosis, and 7 suspected of having unknown origin seen in Ewha Womens University Hospital , during the period from November 1988 to January 1991. In this study 4 suspected of having polycystic ovary and one having ovarian cyst with E2 level of>100pg/ml was eliminated. In summary the results in this study were as follows. 1. In combination of FSH/hMG stimulation followed by hCG the mean number of leading developing follicles(≥10mm) until day +1(one day before aspiration) was highest (p<0.01)in high serum E2 responder patients, followed by intermediate and low responders respectively(i.e., 9.7 ± 3.3 > 7.4 ± 2.3 > 4.0 ± 1.8). In relation to the dosage of stimulation, low E2 responder patients failed to increase the number of follicles even with increased dosage of stimulation. 2. In follicular growth, daily mean diameter of largest follicle increased or correlated significantly with increase of serum E2 levels in all groups of high (r=0.44, P<0.001), intermediater(r=0.61, p<0.001) and low responders(r=0.69, p<0.001) respectively. It was interesting to note that the daily growth rates of largest follicular diameter were all similar among 3 E2 response including low responders, accounting for 1.5 to 3 mm per day regardless of a natural survival law of minority ethnic group such as low responders mostly consisting of smaller distribution(4.3%). 3. Total oocytes and preovulatory oocytes retrieved per cycle were also high in heigh E2 responders, followed by intermediate and low E2 responders respectively (i.e.,4.4 ±2.1 > 3.2 ± 2.2 > 2.3 ± 1.5) (p<0.05). 4. The fertilized and cleaved(dondeptuses) total oocytes retrieved per cycle(women) was slightly increased or correlated with serum E2 levels among high and intermediate E2 responders respectively (p<0.1 and p<0.1). However, there failed to establish any ststistical differences. or correlation in the rates of fetilization or cleavage of preovulatory oocyles among 3 different E2 responders or among 3 terminal E2 patterns of A,G and B. In general, fertilized or cleaved preovulatory oocytes per women(cycle) could be expected to retrieve 2 or more.